A Monster in the Lake! by Bill Grange

Well, a monster which is only 1 millimetre long, but which could easily be a model for some outlandish creature from a Doctor Who episode!

When carrying out a survey of creatures living in the upper lake in Allestree Park with Pat Sear, Steve Plant and myself, we came across a specimen of Polyphemus pediculus. It is a relative of the water fleas, Daphnea - really tiny crustaceans, in the same general group of creatures as crabs, lobsters and shrimps. Unlike Daphnea, though, Polyphemus lacks a shell or carapace. Its bristly legs are employed to catch smaller water fleas, such as Daphnea, so it is a fearsome predator in its own small world. To our eyes, the most odd thing about it is probably the single bulbous eye at the front. This is a compond eye, similar to those of insects and enables the Polyphemus to find prey and to avoid predators which may eat it.

There are two forms, one sexual the other asexual, which co exist. In the asexual form the young develop within the female without being fertilized (pathenogenesis) and a born as fully-functioning miniatures of the parent

In the case of the sexual form the female carries eggs, within a pouch, which have been fertlized by sperm from a male Polyphemus. They are later are released and settle among the sediment.at the bottom of the lake

Polyphemus (named after the one-eyed god of Greek mythology) is apparently common along the margins of muddy lakes, such as Allestree, thoroughout the country, but this is the first time any of us had seen it (or noticed it).

Steve took the specimens of Polyphemus home to photograph them through his microscope.

Polyphemus pediculus

showing the bulbous eye, bristly limbs and several young inside the tranparent body, waiting to be born. You can also see the gut full of food.

Photograph by University of New Hampshire, U.S.A.

Polyphemus pediculus

A line Drawing showing a little more clearly the structures mentioned above. The backwardly directed forked spine is probably a stabililization device to aid in swimming.

From 'Pond Life' by W. Engelhardt, 1964

Polyphemus pediculus

The specimen from Allestree Park Lake.

This is an 'axexua', 'pregnant' female, the young (with their prominent eyes) being seen through her transparent body.

Photo by Steve Plant

Polyphemus pediculus

A specimen from Allestree Park Lake, front view, with a young specimen top right.

Photo by Steve Plant

Polyphemus pediculus

A specimen from Allestree Park Lake, showing a 'sexual' female, with eggs within the pouch. It is surrounded by young produced by a different 'axesual' female.